This study tests the effects on social and emotional development, including attachment, of an infant care pattern that departs from the norm of Westen industrialized society in the direction of patterns of hunting-gathering societies. It follows from findings on the !Kung Bushmen who practice a form of infant care characterized by a large amount of physical contact, very frequent nursing, and immediate response to crying. Two American "subcultures of infant care" are compared: members of the La Leche League--who keep their infants in close physical contact, nurse frequently, and respond quickly to crying-and a matched group who practice a form of infant care more typical of middle-class Western society. Mother-infant interaction is recorded in unstructured settings in the home and structured settings in the laboratory, using a keyboard for continuous recording of timed sequences with automatic translation into computer-readable form. The infants are followed from six weeks to two years of age. The groups are expected to differ in infant-care patterns and features of social and emotional behavior including behavior in the Ainsworth Strange Situation, but not in visual or vocal communication or in cognitive development. The results will be interpreted in terms of Bowlby's evolutionary theory of mother-infant relations and current theory of the effect of early experience on social development.